1. Field of the Invention
The present invention relates to a method of and an apparatus for measuring birefringence, and more particularly, it relates to a method of and an apparatus for measuring birefringence which is suitable for measuring retardation of a composite film, sheet, board or the like. The inventive method of and apparatus for measuring birefringence are particularly useful for measuring retardation and a principal refractive index direction of a liquid crystal phase contrast film, or a film or a sheet consisting of a composite material such as a polymer film which is laminated on a metal surface.
2. Description of the Background Art
In a conventional birefringence measuring apparatus, a photometric part is separated into a light projecting part and a light receiving part which are arranged on both sides of a sample surface respectively. Further, a polarizer and an analyzer which are employed as a set are arranged on the light projecting and light receiving parts respectively. Therefore, it takes much time and labor in order to adjust the polarizer and the analyzer in the same polarization direction in parallel nicol arrangement. This also applies to a case of adjusting the polarizer and the analyzer in relation of prescribed polarization directions such as vertical nicol arrangement.
Further, it is necessary to ensure a large space for installing the apparatus in a production line, since the apparatus is of a transmission type.
In addition, the apparatus is applicable only to light transmittable materials, since the same detects quantities of transmitted light.
Thus, the conventional birefringence measuring apparatus has problems in adjustment of the apparatus, the installation space and restriction of the sample to be measured.